JPS63165721A - Liquid level meter - Google Patents

Abstract

PURPOSE:To enhance detection accuracy, by arranging a displacement detection circuit at the same environmental temp. as a detection part or less. CONSTITUTION:A displacement detection circuit B is arranged at the same environmental temp. as a detection part A or less. Now, when the temp. of the environment where the detection part A is present changes, the coil 11 of the detection part A receives temp. change, and not only the internal resistance and inductance of the coil 11 but also the impedance thereof change. The output corresponding to the change part of the impedance is added to the output part at ambient temp. to be inputted to the circuit B. However, since the circuit B itself is present at the same environmental temp., the impedance of the electronic part incorporated in the circuit B also changes. Electronic part having an electric characteristic capable of setting off the change part of the impedance of the detection part A is selected to constitute the circuit B or a correction circuit requiring no temp. sensor is additionally incorporated in the circuit B to make it possible to display an accurate liquid level 6a on a display part C.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) The present invention relates to a liquid level meter used to detect the level of liquid such as fuel stored in a fuel tank or the like. It is necessary.

(Prior Art) Conventionally, as shown in FIG. 21, a conductive wire 52 is wound around a core 51 to form a tightly wound portion 53 and a sparsely wound portion 54 of a coil 55, and the coil 55 is inserted. There is a liquid level meter 66 in which a conductive ring 65 is loosely fitted on the outside of the casing 56 and the conductive ring 65 is moved up and down in response to fluctuations in the liquid level 60.

In this liquid level meter 66, a change in mutual inductance between the tightly wound portion 53 and the loosely wound portion 54 is output as a change in voltage by the displacement detection circuit 57, and the output is inputted to the display portion 58. It has become. The display section 58 is connected to a power source 67 as well as a displacement detection circuit 57, and is provided with a meter that displays changes in voltage as changes in liquid level 60.

(Problem to be Solved by the Invention) However, in the liquid level meter 66 having the above structure, the liquid 6
4 is rarely kept at a constant temperature.

Therefore, the detection section 61 consisting of the core 51, the tightly wound part 53, the loosely wound part 54, and the conductor ring 65 is affected by the liquid temperature, and the signal input from the detection part 61 to the displacement detection circuit 57 is depends on the temperature.

Therefore, it is necessary to devise a method for outputting the detection part 61 without being influenced by the liquid temperature, and various methods can be considered.

The first method is to use two coils as the primary coil, such as in a differential transformer type or proximity coil type displacement meter, to approximate the temperature coefficient of both, or to adjust the distance between the coils. Therefore, a method of adjusting the reference point can be considered. However, since the liquid level meter 66 has only one primary coil, this method cannot be applied.

A second method is to use a material with a small temperature coefficient for the core 51 and coil 55, but this method has the problem that the material is expensive.

As a third method, as shown in FIG. 22, the temperature of the liquid 64 is detected by a temperature sensor 62 such as a temperature sensitive resistor or a temperature compensation winding, and the output of the displacement 5 detection circuit 57 is corrected by a correction circuit 63. There is.

However, this method requires the temperature sensor 62 and the correction circuit 63.
It is necessary to install both.

Furthermore, in the liquid level meter 66 having the above structure, the displacement detection circuit 57 is usually provided outside the tank 59, so the displacement detection circuit 57 is also affected by the environmental temperature.

For example, if five tanks are maintained at a constant liquid level 60 under various environmental temperatures, the displacement detection circuit 5 at a constant temperature is
When we measure the voltage output from 7, we get a curve like that shown in FIG. Changes to Moreover, the relationship between the two lines c and d is difficult to grasp and is indefinite. This is because temperature changes inside and outside the tank 59 are relatively uneven.

Therefore, each of the detection section 61 and the displacement detection circuit 57 has W.
Even if a correction circuit 63 or the like that operates based on input from the IljJ sensor 62 is incorporated, the detection unit 61 and the displacement detection circuit 57
It is not possible to cancel out the output characteristics with respect to temperature changes.

An object of the present invention is to provide an inexpensive liquid level meter that exhibits excellent detection accuracy despite changes in environmental temperature.

Structure of the Invention (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention adopts a technical means of arranging the displacement detection circuit under the same environmental temperature as the detection section.

(Function) When the temperature of the environment where the detection unit exists changes, the coil of the detection unit changes in temperature, causing the internal resistance and inductance of the coil to change, and as a result, the impedance also changes. The output is added to the output at room temperature and input to the displacement detection circuit.

However, since the displacement detection circuit itself is under the same environmental temperature, the impedance of the electronic components incorporated in the displacement detection circuit also changes.

By configuring the displacement detection circuit by selecting electronic components having electrical characteristics capable of canceling out changes in impedance of the detection section, or by additionally incorporating a correction circuit that does not require a temperature sensor into the displacement detection circuit. , it becomes possible to display accurate liquid level on the display unit.

(First Embodiment) Next, a first embodiment in which the present invention is embodied in a liquid level meter for a fuel tank mounted on a vehicle or the like will be described with reference to FIGS. 1 to 8.

As shown in FIG. 1, a metal upper member 2 having a translucent vertical cross section is welded onto a metal lower member 1 having a concave vertical cross section to form a fuel tank 3 as a liquid storage container. has been done.

An opening 2x is formed at a suitable location in the upper member 2, and a collar-shaped mounting member 4 is placed and fixed onto the opening 2X.

A concave support member 5 is welded and fixed to the bottom surface 1a of the lower member 1, and the lower end of a liquid level gauge 7 is supported on the support member 5. The liquid level 6a of the fuel 6 as a liquid
is now detected.

The liquid level meter 7 of this embodiment includes a detection section A that outputs fluctuations in the liquid level 6a as changes in the inductance of a coil, which will be described later, and a displacement sensor that outputs changes in the inductance of the detection section A as changes in voltage. It consists of a detection circuit B. The detection unit A includes a cylindrical casing 8 with a bottom, a core 9 inserted into the casing 8, a coil 11 formed by winding a conductive wire 10 around the core 9, and a coil 11 formed on the outside of the casing 8. A conductor ring 12 is arranged to loosely fit into the conductor ring 12.

The casing 8 consists of a relatively thin guide portion 8a that guides the conductive ring 12 in the vertical direction, and an enlarged diameter portion 8b formed on the upper part of the guide portion 8a. It is provided within the diameter portion 8b.

A flange-shaped stopper 8C is formed at the lower part of the guide portion 8a, and when the fuel 6 in the fuel tank 3 is discharged and the conductor ring 12 is lowered, the lowering of the conductor ring 12 is stopped by the stopper 8C. It is designed to be stopped by. Note that a projection 8X is provided on the top surface of the stopper 8C.
The conductor ring 12 is formed so that it faces upward.
When the stopper 8C comes into contact with the stopper 8C, the two do not come into close contact with each other.

As shown in FIG. 2, the core 9 has 30 to 50
It consists of a cylindrical body formed by spirally rolling a silicon steel thin plate 13 coated with an inorganic insulating film of .mu.m. This core 9 is inserted into a resin pipe 15 made of polyacetal, polyamide, etc., shown in FIG.

As shown in FIG. 4, in the portion of the resin pipe 15 located at the enlarged diameter portion 8b, a lower member 16 having a substantially brim shape is formed by insert molding, and a short core pipe 17 is formed on the lower member 16. It is fitted onto the resin pipe 15. Note that a notch 22 is provided at the outer edge of the lower member 16.
is provided, and a conductive wire 10 for forming the coil 11 can be inserted therethrough.

Above the lower member 16, a flange-shaped upper member 18 is inserted over the resin pipe 15 at a predetermined interval, and a bobbin 21 is formed. Note that the upper member 18
One of two notches is formed in the inner circumferential edge of the upper member 18 , and by fitting a fitting member 20 integrally formed with the upper end of the core tube 17 into the notch 19 , the upper member 18
is fixed to a resin pipe 15.

The upper member 18 itself is formed from a printed circuit board 42 made of glass fiber reinforced epoxy resin, as shown in FIG.
A displacement detection circuit B is formed by a single flat package IC 23, a transistor 24, and a capacitor 25. The electronic components are selected and assembled in consideration of their temperature characteristics so that the amount of change in impedance at each temperature cancels out the amount of change in impedance of the detection section A.

The coil 11 includes a densely wound portion 11b formed by tightly winding the conducting wire 10, and the conducting wire 10 of the densely wound portion 11b is passed through a notch 22 and wound loosely around the resin pipe 15 below the bobbin 21. It is formed from the formed loosely wound portion 11a.

The conductive ring 12 is attached to the float 14 and is connected to the fuel 6.
It can float upwards.

As shown in FIG. 1, a cap member 27 made of an elastic material is attached to the upper end of the casing 8, and the inside of the casing 8 is kept at the same environmental temperature.

A diaphragm 28 extends outward from the outer periphery of the lower part of the cap member 27, and the periphery of the diaphragm 28 clamps the inner peripheral end of the mounting member 4, so that the upper part of the liquid level gauge 7 can be attached to the fuel tank 3 without wobbling. Retained.

Roughly speaking, a reverse circular protector 2 is mounted on the mounting member 4.
9 is attached to protect the upper part of the liquid level gauge 7.

A lead wire 30 is inserted from the display section C provided outside the liquid level meter 7 into the center of the protector 29 and connected to the conductive pin 26 protruding above the cap member 27 and the connector 31. ing.

Therefore, in this embodiment, as schematically shown in FIG. 7, it can be said that the displacement detection circuit B is installed in the casing 8 under the same environmental temperature as the detection part A. The fuel tank 3 is provided with a supply port for supplying the fuel 6 therein, a vent tube for discharging the fuel 6 (both not shown), and the like.

The displacement detection circuit B is a conversion circuit, as shown in Fig. 6, which inputs a rectangular wave to the R series circuit, detects the inductance of the R series circuit as a time constant, and detects the change in voltage. It is designed to be output as .

An oscillation circuit 44 whose oscillation frequency is determined by a capacitor C1 and a resistor R5 connects to the coil 1 via a buffer operational amplifier 47.
1, so that the oscillation circuit 44 can oscillate a rectangular wave of voltage V'.

A resistor R6 forming an LR series circuit with the coil 11 is connected to the output side of the coil 11. The LR series circuit is connected to the non-inverting input terminal of the comparator circuit 45, and the inverting input terminal of the comparator circuit 45 is connected to resistors R7 and R8 from the power supply voltage.
A reference voltage VS divided by VS is applied.

The output side of the comparison circuit 45 is connected to the emitter of the PNP type transistor 24, and the rectangular wave of the oscillation circuit 44 is applied to the base of the transistor 24.

Further, the output side of the comparison circuit 45 is connected to a smoothing circuit 46 consisting of a resistor R11 and a capacitor C2 via a resistor RIO. The output side of the smoothing circuit 46 is connected to the non-inverting input terminal of an operational amplifier 48, from which the output voltage vb of the displacement detection circuit B is displayed on the display section C.
is input.

Note that carbon film fixed resistors, tantalum film fixed resistors, etc. are used as the resistors R6 and Rs, and aluminum electrolytic capacitors, tantalum capacitors, etc. are used as the tr II capacitors C1 and C2. These are appropriately selected in consideration of the amount of change in inductance, temperature characteristics, internal resistance of the coil 11, temperature characteristics, etc.

Next, the operation and effect of the first embodiment will be described. The liquid level 6a changes depending on the number of fuel 6 stored in the fuel tank 3. Then, the conductor ring 12 of the liquid level meter 7 moves up and down in response to changes in the liquid level 6a.

Since the loosely wound part 11a and the closely wound part 11b of the coil 11 are formed in the casing 8 of the liquid level meter 7 in the vertical direction sequentially from below, the magnetic flux distribution is asymmetrical and perpendicular to the conductor ring 12. The magnetic flux density is highest near the top of the coil 11, and is located in the loosely wound portion 11a, the tightly wound portion 11b, and the conductor 12.
The mutual inductance increases as the conductor ring 12 moves upward, and since the impedance of the conductor ring 12 is low, the inductance seen from the coil 11 decreases. This change in inductance is input to the display section C as a change in voltage by the displacement detection circuit B in the following manner.

A rectangular wave voltage Vf is input from the oscillation circuit 44 to the LR series circuit via the buffer operational amplifier 47.

A voltage Vr that rises with a delay after the high level voltage f is input and falls with a delay after the low level voltage is input is output from the LR series circuit. That voltage V
r is input to the non-inverting input terminal of the comparator circuit 45, and the reference voltage ■S is input to the inverting input terminal. When the voltage r is larger than the reference voltage VS, the comparator circuit 45 outputs a rectangular wave voltage Va, but when the output voltage Vf of the oscillation circuit 44 is at a low level, the voltage va of the comparator circuit 45 is When the voltage Va is absorbed by the emitter side of the transistor 24 and not absorbed by the transistor 24, the voltage Va is absorbed by the smoothing circuit 4.
6 is input. The voltage smoothed by the smoothing circuit 46 is zero-adjusted by the operational amplifier 48 and inputted to the display section C as the output voltage vb of the displacement detection circuit B.

During this process, if the temperature inside the fuel tank 3 changes, the coil 1
1 undergoes a temperature change, its internal resistance and inductance change, and as a result, its impedance also changes. Then, an output corresponding to the change in impedance is added to the output at room temperature and input to the displacement detection circuit B.

However, since the displacement detection circuit B itself is under the same environmental temperature, the impedance of electronic components such as the resistor R5 and the capacitor C1 built into the displacement detection circuit also changes.

However, since the electronic components are assembled in such a way that the amount of change in impedance cancels out the amount of change in impedance of the detection section A after considering its temperature characteristics, the temperature of the fuel 6 in the fuel tank 3 changes. However, the output voltage of the displacement detection section B is temperature-corrected, and the display section C displays an accurate liquid level. Therefore, there is no need to separately provide a correction circuit that requires a temperature sensor.

Even if the amount of change in impedance of the entire electronic components in displacement detection circuit B is a circuit that cannot completely cancel out the amount of change in impedance of detection part A, if displacement detection circuit B is in the same environment as detection part A, Since it is based on the temperature, it is possible to grasp the temperature characteristics of the displacement detection circuit B, and as a result, a correction circuit that can correct the temperature characteristics and does not require a temperature sensor at all can be easily added to the displacement detection circuit B. be able to.

In the displacement detection circuit B of this embodiment, tantalum film fixed resistors are used for the resistor R6 of the LR series circuit and the resistor R8 on the input side of the reference voltage, and a polyester film capacitor is used for the capacitor C1 of the oscillation circuit 44,
When a tantalum capacitor is used as the capacitor C2 of the smoothing circuit 46, the output caused by the temperature change in the detection section A can be canceled out with the similar output in the displacement detection circuit B, as shown in the curve a in Fig. 8. The output voltage of the displacement detection circuit B hardly changed even if the Ij3 ambient temperature changed.

This displacement detection circuit B has a circuit 5 configuration for detecting the inductance change of the detection part A as a time constant and outputting it as a voltage change, and does not include any special configuration for temperature correction.

On the other hand, if carbon film fixed resistors are used for all the resistors, a polyester film capacitor is used for the capacitor C1 of the oscillation circuit 44, and an aluminum electrolytic capacitor is used for the capacitor C2 of the smoothing circuit 46, displacement detection is possible. The output voltage of circuit B changed as the environmental temperature changed as shown by the curve in Figure 8, but the curve did not fluctuate as if the detection section A and displacement detection circuit B were installed separately. There was no. Therefore, it is possible to design a correction circuit that does not require a temperature sensor based on this curve, and by incorporating that correction circuit into displacement detection circuit B, the output voltage can be kept almost constant even if the environmental temperature changes. I was able to do that.

Furthermore, since the displacement detection circuit B is housed within the casing 8, in the present invention, there is no need to provide a separate casing for accommodating them as in the prior art.
This makes it possible to save space and reduce costs.

In this embodiment, since the upper member 18 is also used as the printed circuit board 42 of the displacement detection circuit B, the manufacturing cost of the liquid level meter 7 can be reduced, and the tightly wound portion 11
Wiring work at the b end can be done easily.

(Second Embodiment) Next, a second embodiment in which the present invention is embodied by providing a displacement detection circuit in a different location from that of the first embodiment will be described with reference to FIGS. 8 and 9.

A recess 1y is formed in the center bottom surface of the lower member 1 of the fuel tank 3, and an opening 1x is formed in the center of the recess 1y. The lower end of the liquid level gauge 7 is inserted into this opening 1X, and a seal member 32 seals between the two.

The liquid level meter 7 is composed of the same elements as in the first embodiment, but has a structure similar to the liquid level meter 7 of the first embodiment upside down. That is, the lower end of the casing 8 of the liquid level meter 7 has a lower opening 8 that opens downward.
y is formed.

Inside the casing 8, as in the first embodiment, there are a core 9, a loosely wound portion 11a1 of the coil 1], a densely wound portion 11b, and a bobbin 21.
is inserted. These members are fixed within the casing 8 when the casing 8 is insert molded.

After the terminals of the conducting wire 10 of the coil 11 are soldered to the displacement detection circuit B, the displacement detection circuit B is press-fitted into the lower opening 8y. A lead wire 30 is led from the display section C to the displacement detection circuit B through a fixing member 35 and a grommet 33. After the grommet 33 is press-fitted into the lower opening 8y, it is fixed by screwing a member 34 onto the lower outer periphery of the casing 8.

A protector 29 for protecting the lower end of the liquid level gauge 7 is attached to the lower surface of the lower member 1.

Also in this embodiment, both the detection section A and the displacement detection circuit B are provided in the fuel tank 3, and both exist under substantially the same environmental temperature.

Therefore, the relationship between the environmental temperature and the output voltage of the displacement detection circuit B becomes as shown by the curve a in FIG. 8, and a correction circuit is not required. As a result, even if the temperature of the fuel tank 3 changes, the liquid level 6a is accurately displayed on the display section C.

In addition, the liquid level meter 7 of this embodiment can be advantageously used in cases where it is not possible to attach two protectors to the upper part vi2 of the fuel tank 3, or where it is desired to detect the liquid level 6a down to the lower full scale. Ru.

(Third Embodiment) A third embodiment in which the detection section is mounted in a different manner will be described with reference to FIGS. 10 and 11.

As in the first embodiment, various electronic components are mounted on the printed circuit board 42.
A displacement detection circuit B is formed by assembling the displacement detection circuit B. This displacement detection circuit B is vertically inserted into a core 9 made of silicon steel.

A locking portion 37 formed in a notch 36 formed at the upper end of the resin pipe 15 and extending laterally at the upper end of the displacement detection circuit B is press-fitted.

Other configurations, such as a bobbin 21 attached to the upper part of the resin pipe 15 and a tightly wound portion 11b formed on the bobbin 21, are substantially the same as in the first embodiment.

This embodiment also exhibits the same effects as the above-mentioned embodiments, but in addition, the displacement detection circuit B can be easily and stably installed in the core 9, and can be removed. The effect is demonstrated. Incidentally, even if the displacement detection circuit B is installed in the core 9, the influence of the magnetic field on the displacement detection circuit B hardly becomes a problem.

(Fourth Embodiment) Figure 12 shows a fourth embodiment in which the mounting method of the liquid level gauge to the fuel tank and the mounting method of the displacement detection circuit to the casing are different from those described above. I will explain based on this.

A displacement detection circuit B is provided below the core 9 in the casing 8 of the liquid level meter 7, and the displacement detection circuit B
A lead wire 30 passes through the core 9 and is electrically connected to the display section C.

Two guide members 38 are formed to protrude outward in the diametrical direction on the outer peripheral surface of the enlarged diameter portion 8b of the casing 8.

A cap-shaped support member 40 is mounted on the cap member 27 mounted on the enlarged diameter portion 8b via a coil spring 39 for urging the liquid level gauge 7 downward.

This cap-shaped support member 40 is held by the protector 29 of the upper member 2 via the seal member 32. A vertically long notch 41 for guiding the guide member 38 is formed in the side wall of the cap-shaped support member 40 .

A connector 31 of the lead wire 10 extending from the displacement detection circuit B is attached to a portion of the cap-shaped support member 40 that projects upward from the protector 29, and a lead wire extending from the display portion C is attached to the connector 31. 3
0 is joined.

The other configurations are almost the same as in the first embodiment, and the displacement detection circuit B is located at the same environmental temperature as the detection section.

In this embodiment, the detected liquid level 6a is accurately displayed on the display section C even if the environmental temperature changes. Roughly,
The liquid level gauge 7 is constantly controlled by the coil spring 39.
Since it is biased downward, even if the fuel tank 3 thermally expands and the lower member 1 swells downward and the liquid level 6a decreases, the liquid level gauge 7 follows the lower member 1. Descend.

Therefore, measurement errors in the liquid level 6a can be suppressed.

(Fifth Embodiment) A fifth embodiment in which the support structure of the lower end of the liquid level meter with respect to the fuel tank and the support structure of the displacement detection circuit with respect to the liquid level meter are made different from each other will be described based on FIG. I'll explain.

A recess 1 is provided on the bottom surface 1a of the lower member 1 in the fuel tank 3.
y is formed, and a concave support member 5 is fixed to the concave portion 1y by spot welding.

A female thread 5a is formed on the inner surface of the support member 5, and the lower end of the casing 8 of the liquid level gauge 7 is screwed into the female thread 5a. Since there is no support member above the liquid level gauge 7 to support it on the fuel tank 3,
In this embodiment, the liquid level gauge 7 is supported only by the support member 5.

The displacement detection circuit B is fixed within the cap member 27 when the cap member 27 is insert-molded, and the cap member 27 is welded above the enlarged diameter portion 8b of the casing 8.

The printed circuit board 42 of the displacement detection circuit B is made of a heat-resistant resin such as polyimide resin so as to withstand insert molding of the cap member 27.

In this embodiment as well, the displacement detection circuit B exists under the same environmental temperature in the fuel tank 3 as in the detection section. The other configurations are almost the same as those of the first embodiment.

In this embodiment as well, the output of the detection section A caused by the temperature change in the fuel tank 3 is offset by the output of the displacement detection circuit B, which is also caused by the temperature change. Roughly speaking, in this embodiment as well as in the second embodiment, the liquid level 6a is accurately detected until it becomes substantially zero.

The present invention is not limited to the above embodiments, but includes, for example,
It can also be embodied in the following manner.

(1) When the displacement detection circuit B is provided on the back side of the cap member 27 of the enlarged diameter portion 8b of the casing 8, the first
As shown in FIG. 4, a leg-shaped or cylindrical locking protrusion 43 is provided on the back side, and a displacement detection circuit B is provided on the locking protrusion 43.
The printed circuit board 42 may be locked.

(2) When the displacement detection circuit B is provided in the lower part of the casing 8, it can be integrally molded with the casing 8 as shown in FIG. In this case, only the portion of the guide portion 8a of the casing 8 below the stopper 8C is separately insert-molded using the displacement detection circuit B as an insert, and the obtained molded body is welded to the cylindrical portion that will become the guide portion 8a. By doing so, the displacement detection circuit B can be attached to the casing 8.

(3) As shown in FIG. 16, a notch 19 is formed on the inner peripheral edge of the printed circuit board A2, and a fitting member 20 formed separately from the core tube 17 is inserted between the notch 19 and the resin pipe 15. By inserting the printed circuit board 42, the printed circuit board 42 can be fixed to the resin pipe 15.

(4) As shown in FIG. 17, the lower member 16 and the upper member 18 may be adhesively fixed to the upper and lower end surfaces of the core tube 17 or to the outer peripheral portions of the upper and lower ends.

(5)' As shown in FIG. 18, a mock fitting member 20 is driven between the upper member 18 and the resin pipe 15,
The upper member 18 can also be fixed to the resin pipe 15.

(6) As the displacement detection circuit B, a comparator can be used instead of the operational amplifier in the first embodiment (FIG. 6). In addition, as shown in FIG. 19, the first embodiment (sixth
It is also possible to configure the displacement detection circuit B by using a buffer transistor 24 in place of the buffer operational amplifier 47 shown in the figure, and by using a comparator 49 in place of the transistor 24 in the first embodiment. In this case, a filter capacitor C3 for removing ripples is placed on the output side of the comparator 48a.
will be established. This filter function may be performed by the negative feedback section of the comparator 48a.

In this displacement detection circuit B, if you pay attention to the impedance of the amplification stage, the displacement detection circuit B of the first embodiment requires a power supply voltage higher than the maximum output voltage in consideration of the output saturation level of the operational amplifier. On the other hand, the power supply voltage may be approximately the same as the maximum output voltage. For example, when it is desired to change the output voltage from 0 volts to 5 volts 1-, in the case of the first embodiment, a power supply voltage of 7 volts is required, but in FIG. 19, approximately 5 volts is sufficient.

In this displacement detection circuit B, all the resistors of the oscillation circuit 44, the resistor R6 of the L and R series circuit, the resistors R1 and R8 on the inverting input terminal side of the comparator circuit 45, the resistor R11 of the smoothing circuit 46, and the resistor R13 on its input side , and a tantalum film fixed resistor for the input power supply resistor R17 on the filter capacitor C3 side, a carbon film fixed resistor for the other resistances, a polyester film capacitor for the capacitor C1 of the oscillation circuit 44, and a smoothing circuit. When tantalum capacitors are used for each of the 46 capacitors C2, the output voltage vb from the displacement detection circuit B can be kept almost constant even if the environmental temperature changes over a wide range, as shown by curve a in Figure 8. can.

(7) As shown in FIG. 20, the oscillation circuit 44 is made to oscillate by connecting the coil 11 and the resistor "18 to the feedback circuit of the oscillation operational amplifier 50, and the frequency f of the oscillation circuit 44 changes as the inductance of the coil changes. It is also possible to calculate changes in the liquid level 6a with a microcomputer and digitally display the changes in the liquid level 6a.However, since this circuit has a small number of electronic components, it may not be possible to offset the changes due to the environmental temperature. The liquid level 6a can be accurately detected by incorporating the correction circuit together with the displacement detection circuit B in the environment where the detection section A exists, or by combining electronic components in consideration of their temperature characteristics.

(8) Among the electronic components used in the displacement detection circuit B, a nickel-chromium film fixed resistor, a temperature sensitive resistor with a temperature detection film, etc. can be used as the resistor R.
In addition, as capacitors, metallized polyester film capacitors, polypropylene film capacitors,
Metallized polypropylene film capacitors, TF capacitors, etc. can be used in consideration of temperature characteristics and frequency characteristics.

(9) The liquid level meter 7 according to the present invention is particularly suitable for use in the fuel tank 3 of a vehicle, and is required to measure the liquid level 6a while eliminating the influence of environmental temperature. As a total of 7, it can be effectively used in various fields.

(10) If the displacement detection circuit B is installed at substantially the same environmental temperature as the detection part A, it can be provided at a location other than the casing 8.

Effects of the Invention As detailed above, the present invention enables a liquid storage container to accurately detect and display the liquid level without error even if the temperature of the liquid changes due to changes in environmental temperature or the like. It shows excellent results.

Further, the present invention exhibits the effect that a temperature sensor is not required even when the correction circuit is provided in the displacement detection circuit.

Furthermore, since there is no need to provide a special casing for accommodating the displacement detection circuit, the liquid level meter according to the present invention has a compact shape and can be manufactured at low cost.

[Brief explanation of the drawing]

Figures 1 to 20 are drawings according to the present invention, where Figure 1 is a longitudinal sectional view of the first embodiment, Figure 2 is a perspective view of the core used in the first embodiment, and Figure 3 is a resin pipe. FIG. 4 is an exploded perspective view of the bobbin, FIG. 5 is a perspective view of the bobbin assembled to the core, FIG. 6 is a circuit diagram of the displacement detection circuit,
Fig. 7 is a schematic explanatory diagram of the first embodiment, Fig. 8 is a diagram showing the relationship between the environmental temperature and the output voltage of the displacement detection circuit, Fig. 9 is a longitudinal cross-sectional view of the second embodiment, and Fig. 10. is a longitudinal sectional view of the main part of the third embodiment, FIG. 11 is a perspective view of the main part, FIG. 12 is a longitudinal sectional view of the third embodiment, and FIG. 13 is a longitudinal sectional view of the fourth embodiment.
FIG. 14 is a longitudinal cross-sectional view of a main part showing another way of mounting the displacement detection circuit on the upper part of the casing, FIG. 15 is a longitudinal cross-sectional view of the main part showing another way of mounting the displacement detection circuit on the lower part of the casing, and FIG. The figure is a perspective view showing a mode of attachment of the upper member in which the displacement detection circuit is assembled, FIG. 17 is a perspective view showing another mode of attachment of the upper member, and FIG. is a perspective view showing an embodiment, FIG. 19 is an electric circuit diagram showing another embodiment of the displacement detection circuit, FIG. 20 is an electric circuit diagram similarly showing another embodiment, and FIG. 21 is a longitudinal sectional view of the conventional technology. FIG. 22 is an explanatory diagram as well, and FIG. 23 is a diagram showing the relationship between environmental temperature and output voltage in the prior art. 3... Liquid storage container, 6... Liquid, 6a... Liquid level, 8... Casing, 9... Core, 10...
...Conducting wire, 11...Coil, 12...Conductor ring, A...Detection section, B...Displacement detection circuit

Claims (1)

[Claims] 1. Core (9) inserted into cylindrical casing (8)
a coil (11) formed by winding a conductive wire (10) around the core (9); and a liquid storage container (11) that is loosely fitted into the casing (8) on the outside of the coil (11). 3) Conductor ring (12) floating on top of liquid (6) inside
A detecting section (A) is configured to detect a change in the liquid level (6a) of the liquid (6) as a change in the inductance of the coil (11), and a displacement detecting circuit is provided in the detecting section (A). (B), wherein the displacement detection circuit (B) is arranged under the same environmental temperature as the detection part (A). 2. The liquid level meter according to claim 1, wherein both the displacement detection circuit (B) and the detection section (A) are housed in the casing (8).